1. Field of the Invention
The present invention relates generally to regulating delivery of minute quantities of liquids, and more specifically to microfluidic systems particularly for analytical instruments such as those used for DNA or peptide sequencing and medical or clinical diagnostics.
2. Description of the Prior Art
Various efforts are underway to build miniature valves and pumps in silicon for micro-fluidics. It is however proving to be difficult to produce good sealing surfaces in silicon, and it turns out that these valves, although in principle mass-produced on a silicon wafer, become expensive in their packaged finished form. Consequently, such micro-fluidic components can hardly be considered inexpensive and/or disposable. Moreover, in such micro-fluidic components liquid contacts the valve and pump bodies and passages, thereby creating a contamination problem if the micro-fluidic component is to be reused. In addition, these micro-fluidic valves still must be interconnected into systems, and such interconnection also becomes expensive.
This interest in micro-fluidic components has been spurred largely by the rapid developments in the medical and biological sciences and related fields. In many such applications, small amounts of liquids need to be dispensed, samples need to be introduced and mixed in a given sequence with a variety of reagents, and the reagent products need to be examined for the presence or absence of particular species. In addition, obtaining good analytic results often requires that the dead volume associated with valving and tubing be extremely small.
Examples of processes which would benefit from a micro-fluidic system are immunoassay tests, or DNA tests for forensic applications, infectious or genetic diseases or screening for genetic defects. These tests often involve the polymerase chain reaction ("PCR") which is used to multiply strands of DNA many fold thereby obtaining sufficient material for standard analytic techniques. For many clinical applications, it is highly desirable to perform tests in a doctor's office rather than at a remote laboratory, thereby saving the costs and time of sample preservation, contamination and transportation. Hence portable, small, fully integrated systems, capable of performing these complex tests are highly desirable.
For these types of analytic systems, it is often desirable to incorporate some of the reagent liquids into the system thereby reducing local operations, and to guarantee that the reagents have the same quality as originally provided by their manufacturer. In many cases, it is desirable that the unit be completely automated, and that only the sample liquid need be introduced into the system. It is also often advantageous to perform a battery of tests on the same sample, either simultaneously or sequentially.
In the case of analytical instrumentation, large quantities of liquids may be required, more than can be conveniently stored in a micro-fluidic system. However, it is still highly desirable under such circumstances that the complex array of interconnections of very small tubes, valves etc. be replaced by an integrated system which is much less prone to leakage, dead-space and contamination, and that costs substantially less.
Presently, an area of materials research identified as combinatorial synthesis seeks to synthesize as possible pharmacuticals "polymeric" materials that consist of an arbitrary, but pre-specified sequence, assembled from different monomeric starting materials. Extending the concept of the four DNA base pairs that make up genetic material and the twenty amino acids that make up all proteins, this area of chemical synthesis seeks to synthesize such polymeric materials, one monomeric unit at a time, an chain of monomeric units chosen arbitrarily from as many as two hundred different monomers. It is readily apparent that assembling a system to perform combinatorial synthesis using conventional laboratory apparatus is a herculean task.